During the coming year, we will work on three major projects. In one, we will carry out breeding studies to determine whether the production by certain A/J mice of anti-Ar antibodies containing a low concentration of a cross-reactive idiotype is an inherited characteristic. Large numbers of mice will be immunized and those producing low concentrations of the cross-reactive idiotype will be selected for further mating studies. Within two or three generations, it should be possible to ascertain whether the production of low concentrations of idiotype is an inherited characteristic. If so, it would have profound implications with regard to the nature of the portion of the genome which contains the V-region genes. A second project will be devoted to the production of anti-Ar antibodies bearing a high concentration of antiidiotypic antibodies. There is already evidence in the literature that B cells can be stimulated by antiidiotypic antibodes. We will use antiidiotypic antibodies, directed to the anti-Ar antibodies of A/J mice, prepared in guinea pigs and in rabbits. The guinea pig antibodies will be fractionated into the IgG1 and IgG2 subclasses and the rabbit antibodies will be degraded to F(ab')2 fragments; the latter step is necessary because rabbit IgG suppresses the idiotype. A third set of investigations will be devoted toward the development of methods for producing the molecules bearing the idiotype in tissue culture. Studies will be carried out with fragments of spleen or lymph nodes and in single cell suspensions. We have already developed our radioimmunoassay so that it can detect as little as 2 ng of anti-Ar antibodies bearing the cross-reactive idiotype. Efforts will be made to make the procedure even more sensitive. The development of a tissue culture system would greatly expedite studies on the factors that control the synthesis of the idiotype.